Conventional railroad cars are generally constructed with a body having an underframe that includes a pair of spaced-apart body bolsters resting on and rotatably or swivelly received by a pair of spaced-apart trucks that rollingly support the car along railroad tracks. Each body bolster is swivelly or rotatably received by a truck bolster by a conventional center plate assembly that includes a body bolster center plate on the underframe, a truck bolster center plate on the truck, and a liner or wear element between the center plates. A conventional kingpin extends through the center plates.
Heretofore, it has been well known in the railroad industry to use manganese steel liners as wear elements in center plate assemblies. These steel liners, of course, provide electrical continuity between the body bolster center plate and the truck bolster center plate or bowl. It has also been known to employ plastic center plate wear liners between the body bolster center plate, and the truck bolster center plate to reduce wear on these parts by eliminating the metal-to-metal contact incurred with steel liners as well as providing self-lubrication between these parts. These liners have included both horizontal or disk-shaped liners, as well as cup-shaped or bowl-shaped liners.
However, it is necessary to retain some metal-to-metal contact to create electrical continuity or conductivity between the plates. This continuity is important because it provides a ground for the car body, thereby eliminating the buildup of static electricity on the car body. Additionally, the electric continuity provides the ability to obtain signals through the tracks. The metal-to-metal contact that created the continuity in plastic wear liners has been generally provided by brass, copper, or other electrically conductive studs or pins placed in the plastic liner extending between both sides to engage both plates which provide the electrical continuity but increase the friction between the plates. Moreover, the heads of the studs or pins tend to break or wear off and then become less effective to provide electrical continuity.
It has also been known to add conductive fillers or steel mesh to plastic materials to make them electrically conductive. However, the addition of conductive fillers, such as carbon black or fibers, materially weakens the integrity and wearability of the plastic.